The present invention relates to balloon catheters and, more particularly, to a non-shortening wrapped balloon configured to expand to a predetermined diameter upon application of a predetermined pressure thereto.
Balloon catheters are well known in the art. Such catheters are employed in a variety of medical procedures, including dilation of narrowed blood vessels, placement of stents and other implants, temporary occlusion of blood vessels, and other vascular uses.
In a typical application, the balloon is advanced to the desired location in the vascular system. The balloon is then pressure-expanded in accordance with a medical procedure. Thereafter, the pressure is removed from the balloon, allowing the balloon to contract and permit removal of the catheter.
Procedures such as these are generally considered minimally invasive, and are often performed in a manner which minimizes disruption to the patient's body. As a result, catheters are often inserted from a location remote from the region to be treated. For example, during angioplasty procedures involving coronary vessels, the balloon catheter is typically inserted into the femoral artery in the groin region of the patient, and then advanced through such vessel into the coronary region of the patient. These catheters typically include some type of radiopaque marker to allow the physician performing the procedure to monitor the progress of the catheter through the body. As a characteristic of wrapped balloons, it is also common to have the length of the wrapped balloon change during inflation causing placement problems during procedures. Additionally, catheters have been unable to deliver balloons with large diameters expansion capability due to the need for a low profile and sustained high pressures.
There are two main forms of balloon catheter devices. Non-compliant catheters employ a balloon made of relatively strong but generally inelastic material (e.g., polyester) folded into a compact, small diameter cross section. These relatively stiff catheters are used to compact hard deposits in vessels. Due to the need for strength and stiffness, these devices are rated to employ high inflation pressures, usually up to about 8 to 18 atmospheres. They tend to be self-limiting as to diameter in that they will normally distend up to the rated diameter and not distend appreciably beyond this diameter until rupture due to over-pressurization. While the inelastic material of the balloon is generally effective in compacting deposits, it tends to collapse unevenly upon deflation, leaving a flattened, wrinkled bag, substantially larger in cross section than the balloon was when it was originally installed. This enlarged, wrinkled, relatively stiff bag may be difficult to remove, especially from small vessels.
By contrast, compliant catheters employ a soft, very elastic material (e.g., natural rubber latex) as the balloon. These catheters are employed to displace soft deposits, such as thrombus, where a soft and tacky material such as latex provides an effective extraction means, and also can be used as an occlusion balloon, though operate at low pressures. Latex and other highly elastic materials generally will expand continuously upon increased internal pressure until the material bursts. As a result, these catheters are generally rated by volume (e.g., 0.3 cc) in order to properly distend to a desired size. Although relatively weak, these catheters do have the advantage that they tend to readily return to their initial size and dimensions following inflation and subsequent deflation.
Some catheter balloons constructed of both elastomeric and non-elastomeric materials have been described previously. U.S. Pat. No. 4,706,670 describes a balloon dilatation catheter constructed of a shaft made of an elastomeric tube and reinforced with longitudinally inelastic filaments. This device incorporates a movable portion of the shaft to enable the offset of the reduction in length of the balloon portion as the balloon is inflated. One improved balloon is disclosed in U.S. Pat. No. 4,706,670 teaching reinforcing filaments in a balloon portion at an angle which is less than 54.73 degrees relative to the axis of the balloon. As the length of the balloon portion decreases, the length of the movable portion of the outer tubing increases and by proper selection of internal diameters and lengths of the two portions, the shortening of the balloon is offset.
U.S. Pat. No. 5,647,848 teaches a structure formed of helically extending fibers, including bundles of continuous monofilaments, aramide, polyethylene, steel, polyester, glass, carbon, and ceramics. The fibers are positioned in an elastomer such that the fibers lie at an angle which is less than a neutral angle of 54.73 degrees relative to the axis of the balloon when the balloon is unpressurized. With the utilization of rigid fibers the balloon will be non-compliant in its fully inflated state. The difference in rigidity although desirable with respect to independent movement of the components of the balloon can introduce unwanted torsional moments into the elastomeric balloon depending upon the construction of the balloon and fibers.
Accordingly, there is a need in the art for a soft, high pressure, large diameter, high expansion ratio (greater than 400 percent) balloon which does not lengthen or shorten upon inflation and has a predefined maximum expanded diameter. This maximum expanded diameter should remain constant even as the pressure of the balloon is increased. Moreover, this maximum expanded diameter should remain essentially constant upon repeated inflation and deflation of the balloon. The present invention fulfills this need.